(cell hybridization/cell surface antigens/immunogenetic analysi

Through hybridization of specific Chinese hamster cell auxotrophs with human cells and selection in media lacking the nutritional supplements required by the former cells, a series of stable hybrid clones can be prepared. These hybrids have genomes consisting of a common part- the complete or almost complete set of Chinese hamster chromosomes, plus a variable part-one or a few human chromosomes. The identity of the human chromosomes can be varied by utilizing different Chinese hamster auxotrophs and the appropriate selective media. The human chromo- somes present can be determined by a combination of cyto- genetic analysis with chromosome banding and testing for specific human marker genes. Hybrids containing single human chromosomes 11 and 12 and the combination of both 11 and 12 are described. The system appears to lend itself to various studies such as identification of human cell surface antigens, determination of their chromosomal loci, measure- ment of their distribution among cells of normal human tissues, study of interrelations among syntenic and asyntenic genes, and mutational analysis of the human genome. In previous studies, a series of human-Chinese hamster cell hybrids was produced by fusion of specific Chinese hamster mutant auxotrophs with human cells and growth in selective media lacking the nutrients required by the Chinese ham- ster auxotroph (1-5). The clones developing under these se- lective conditions must retain the human chromosomes com- plementing the deficiency of the Chinese hamster cell mu- tant employed. By using a variety of such Chinese hamster mutants, hybrids can be prepared containing different com- plements of human chromosomes. These hybrids tend to lose human chromosomes rapidly, so that in appropriate selective media, as few as one or two human chromosomes have been retained in particular hybrid clones. While the initial pres- ence of a selective medium is usually necessary to ensure re- tention of a particular human chromosome, hybrid clones are sometimes obtained with stable chromosomal constitu- tion after a short period of growth in culture, so that thereaf- ter the clones can be grown for long periods even in nonse- lective media without further loss of human chromosomes (2, 5). It was also shown that antisera to tissue culture cells can be produced in the rabbit and other animals which are ac- tive against cell surface antigens and produce lethal effects in the presence of complement (2, 5-7). When this lethal ac- tion is measured by means of single cell survival curves, the amount of antiserum needed to produce killing is extremely